Gapped magnetic cores are well known in the art. An example of a gapped magnetic core is shown in FIG. 14. In FIG. 14, a magnetic core 2 comprises a portion made of a first permeable material 4 having a relative magnetic permeability μR1>1 and a gap 6 comprising a second material having a relative magnetic permeability μR2<μR1. In a typical example, the first magnetic material might be a ferrite having a μR1>100 and the second material might be air, plastic or epoxy having a μR2=1.
In the absence of a gap, energy storage in a permeable core may be limited by the onset of core saturation. By including a gap in the magnetic core, the amount of energy that may be stored in a given volume at a given flux level may be increased.
Gaps may provide for improved inductive energy density but are not without drawbacks. One problem associated with gaps may be the presence of fringing fields in the region of the gap. FIG. 15, for example, shows a schematic side view of magnetic lines of flux in the region of the gap 6 of the magnetic core 2 of FIG. 14. As shown in FIG. 15, the flux, illustrated schematically by the dashed arrows, is essentially fully constrained within the confines of the relatively high permeability first material 4 but may “fringe” out into the region surrounding the low permeability gap 6. If the length of the gap (dimension G, FIGS. 14, 15) is very small, the amount of fringing may be small. As the gap 6 is made larger, however, the fringing field may spread out further in the region of the gap 6. This may cause a variety of problems: for example, time varying flux in the fringing field may couple into nearby circuitry causing interference and heat losses.
A variety of methods may be used to set discrete gaps in magnetic structures. In one method, one or more discrete gaps are formed by controlling the physical relationship between two magnetic core pieces. For example, the magnetic core 8 of FIG. 16 comprises two magnetic core pieces 10, 12. Two gaps 14, 16 may be formed at the two locations at which the two magnetic core pieces are joined. It may be important to carefully control the length of the gaps to produce desired values for inductance per turn and energy storage capacity of the resulting magnetic core 8. One way to control the length of the gaps may be to use epoxy that is loaded with non-permeable, non-conductive, spherical bodies (e.g., glass or plastic) of a fixed diameter (e.g., 0.4 mil to 10 mil). For example, glass spheres manufactured by Potters Industries Inc., Valley Forge, Pa. USA may be suitable for use in such an application. As the core pieces are brought together, the gaps may be limited to the diameters of the spherical bodies in the epoxy. Another way to form gaps may be to glue spacers of pre-determined thickness between the core pieces, however this may require careful control over the thickness of the glue line. Yet another way to set a gap is to place adhesive in the regions of the gaps and mechanically adjust the gaps between the core pieces 10, 12 while measuring the inductance of the magnetic core 8. When the inductance reaches a pre-determined value the adjustment may be stopped and the adhesive may be allowed to set.
One way to achieve the benefits of a relatively large gap may be to distribute the gap over the length of the magnetic core in the form of a plurality of smaller gaps. By combining several small gaps, substantially increased energy storage may be achieved with, for example, lower fringing field effects than might otherwise be associated with a single, larger, gap.
The use of discretely distributed (also known as quasidistributed) gaps in magnetic cores is discussed generally in Jiankun Hu and Charles R. Sullivan, The Quasi-Distributed Gap Technique for Planar Inductors: Design Guidelines, IEEE Industry Applications Society, Annual Meeting (Oct. 5, 1997) and in Jiankun Hu and Charles R. Sullivan, AC Resistance of Planar Power Inductors and the Quasidistributed Gap Technique, IEEE Transactions on Power Electronics (July 2001).
The use of laser material processing with water-jet technology (the process is known as laser Microjet® dicing) has been described generally in Bernold Richerzhagen, Industrial Applications of the Water-Jet Guided Laser, The Industrial Laser User (September 2002). The use of adhesive tapes with laser Microjet® dicing has been described generally in Pressure-Sensitive Adhesive Tape for Water Jet-Guided Laser Dicing Process, Furukawa Review, No. 22 (2002).
Each of the above mentioned references are hereby incorporated by reference in their entireties.